1. Field of the Invention
The invention relates to a process for preparing compositions comprising a major amount of soap and a minor amount of acyl isethionate.
2 The Prior Art
Soap is an excellent cleaning agent but is quite harsh to the skin. A study by Frosh & Kligman, J. Amer. Acaderm. pp. 35 (1979), revealed that substantial replacement of soap with an alternative detergent such as an acyl fatty isethionate would provide a more skin compatible system. Unfortunately, this alternative is expensive. Less costly solutions are needed to provide the consumer with an economical, yet mild, product.
One approach to resolving the problem has been reported in U.S. Pat. No. 4,695,395 (Caswell et al.). The patent reports that bars containing a major amount of soap and a minor amount of acyl isethionate can be rendered relatively non-irritating by incorporation of non-acylated sodium isethionate. On the heels of this discovery, there was presented a need for a process to prepare such compositions.
U.S. Pat. No. 4,663,070 (Dobrovolny et al.) discloses a batch process wherein a reactor containing a major amount of soap, a minor amount of C.sub.10 -C.sub.16 acyl isethionate, sodium isethionate, water, stearic acid, sodium chloride and certain minor additives are heated at 210.degree.-218.degree. F. under agitation. The reaction was judged as complete and terminated when the blend had passed a second peak in viscosity.
A related case, U.S. Pat. No. 4,707,288 (Irlam et al.) reports an essentially identical formulation prepared in a reactor under conditions of shear maintaining a temperature of from 60.degree. C. to about 90.degree. C. Thereafter, the composition is feed to a plodder and extruded to form a detergent bar.
Each of the foregoing processes begin with soap as a starting material. A necessary condition for the soap/acyl isethionate based mixing is the need for certain initial levels of water. Without a minimum water level in the raw materials, blending would be difficult and gritty product would result. A disadvantage of the aforementioned processes containing water is that moisture must be reduced through evaporation to arrive at an acceptable end product. There is a critical window of moisture beyond which bar physical properties are adversely affected. A second problem with the aforementioned processes is the time required in blending soap with acyl isethionate before there can be achieved the appropriate product viscosity.
Elimination of a drying step has long been known in the soap making art. For instance, U.S. Pat. No. 2,578,366 (Mills) meters an aqueous sodium hydroxide stream and a fatty acid slurry stream into a mixing reactor. Typically, the aqueous solution of caustic soda is maintained at about 80.degree.-95.degree. F. Temperatures for the neutralization and subsequent soap mixing range from about 130.degree. to 215.degree. F.
Along similar lines, U.S. Pat. No. 3,657,146 (Framson et al.) reveals a method for the direct production of soap from fatty acid under reaction temperatures of 120.degree.-180.degree. C. Separate streams of tallow/coconut (80/20) fatty acids, of stoichiometric amounts aqueous sodium hydroxide, and of sodium chloride are pumped into a reactor vessel.
In principle, it would appear attractive to form soap in situ, neutralizing fatty acid, while simultaneously feeding acyl isethionate into the blend. However, there is a problem. Acyl isethionate is susceptible to hydrolysis. Thus, before such a route were to be feasible, ways had to be found to reduce the hydrolysis threat.
Accordingly, it is an object of the present invention to provide a process for preparing toilet bars containing a major amount of soap and a minor amount of acyl isethionate.
A further object of this invention is to provide a method for producing a soap/acyl isethionate bar which substantially eliminates the need for drying and thereby increases production rates.
A still further object of this invention is to provide a process for preparing soap/acyl isethionate compositions by a route which minimizes hydrolysis of the acyl isethionate component.
Another object of the present invention is to provide a process yielding a soap/acyl isethionate composition having consumer use and toilet bar processing properties that fall within commercially acceptable parameters.
These and other objects of the present invention will become apparent as further details are provided in the subsequent discussion and Examples.